Combustion apparatus with ultrasonic vibrator

ABSTRACT

A combustion apparatus is provided of the type comprising an outer air duct with a liquid fuel atomizing horn housed within the outer air duct coaxially thereof. The atomizing horn is vibrated by an ultrasonic vibrator. An inner air duct is located within the outer air duct coaxially thereof between the front portion of said horn and said outer air duct. Inner vanes or air swirling vanes are located within said inner air duct. Outer vanes or air swirling vanes are located between said inner and outer air ducts. An outwardly diverging frustoconical cap is attached to the front open end of the outer air duct. The front portion of the cone-shaped cap is radially inwardly bent to define a center opening; the tips of the inner air swirling vanes are separated from each other and spaced apart from the front end portion of the horn; the ratio of an angle theta 1 minus 10 between the outer and inner air swirling vanes and the axis of the horn to an angle theta 2 or oblique angle between the tapered portion of the cap and the axis of the horn is between 3/10 and unity; and the ratio of the diameter of the center opening of the cap to a length in the axial direction of the frustoconical cap is between 1.25 and 3.

United States Patent Rokudo et a1. Sept. 9, 1975 [54] COMBUSTION APPARATUS WITH [57] ABSTRACT ULTRASONIC VIBRATOR A combustion apparatus is provided of the type com- [75] Inventors: NerumilSU R N r oshiyuki prising an outer air duct with a liquid fuel atomizing lshiguro, Tenri; Makom L horn housed within the outer air duct coaxially lkoma, of Japan thereof, The atomizing horn is vibrated by an ultra- [73] Assigneec Matsushita Electric Industrial Co sonic vibrator. An inner air duct is located within the Osaka Japan outer air duct coaxially thereof between the front portion of said horn and said outer air duct. Inner vanes 1 Filedi 9, 1973 or air swirling vanes are located within said inner air [2]] Appl Na: 414,417 duet. Outer vanes or air swirling vanes are located be tween said inner and outer air ducts. An outwardly diverging frustoconical cap is attached to the from open [30] Foreign Application Priority Data end of the outer air duct. The front portion of the Nov. 17, 1972 Japan 47-1 15816 Cons-Shaped p is radially inwardly I0 define center opening; the tips of the inner air swirling vanes [52] US. Cl 431/1; 239/102 are separated from each other and spaced apart from 5 1 [m (1 H 3053 3/14; F23C 3/00 the front end portion of the born; the ratio of an angle 58] Fi ld f S h 431/1; 239/4 [02 6, minus 10 between the outer and inner air swirling vanes and the axis of the horn to an angle 6 or [56] References Cited Oblique angle between the tapered portion of the cap UNITED STATES PATENTS and the axis of the horn is between 3/10 and unity; s 200 1:73 8/1965 Young ct a1 239 4 x and the ram Of the.diamee.r of i 9 Opening of 51 1 6/1966 g N 43] X the cap to a length 1n the axial direction of the frusto 3,275,059 9/1966 McCullough 239/4 x Coma Cap heween 3,796,536 3/1974 Hori Ct 211 431/1 4 Claims, 14 Drawing Figures PATENTEDSEP ems, 3,904,347

sum 1 OF 4 PATENTED 91575 SHEU 2 [JF FIG. 3

FIG. 4

PATENTEDSEP 91975 a 904 34? saw 3 OF A 60- r AREA Y2 50- E3 4oq AREA p AREA 1 1 l l t i0 20 30 40 50 6O 70 Hr IN DEG.

50 (9 w 40 D g 30 I 1 IO 20 6| IN DEG,

PATENTEDSEP arms 3 0 47 sum u or 9 FIG. 7A

COMBUSTION APPARATUS WITH ULTRASONIC VIBRATOR BACKGROUND OF THE INVENTION The present invention relates to a combustion appa ratus with a horn which is vibrated by an ultrasonic vibrator for atomizing liquid fuel, the kinetic energies of atomized fuel particles are insufficient to propel them forcefully out of the apparatus so that they start to fall immediately from the atomizing surface of the horn. Consequently air is blown from the back of the horn to scatter the atomized fuel particles in the forward direction. In order to facilitate the mixing of atomized fuel particles with air and the formation of a pattern of distribution of atomized fuel particles optimized for complete combustion, inner and outer air swirling vanes are located around the front end portion of the horn so as to swirl the air flows, and an outwardly diverging frustoconical cap is attached to the open front end of an outer air duct to control a flame pattern. However, if the ratio of the angle 8, between the outer and inner vanes and the axis of the horn to an angle 9 or oblique angle between the tapered portion of the frustoconical cap and the axis of the horn. and the ratio of the diameter D of a center opening of the cap to the length L in the axial direction thereof are not within predetermined ranges, incomplete combustion results.

SUMMARY OF THE INVENTION Briefly stated, in accordance with the present invention. the tips of the inner air swirling vanes are separated from each other and spaced apart from the front end portion of the fuel atomizing horn to define an air passage therebetween; the ratio of the angles 0, minus and 6 is being between 3/10 and l; and the ratio between the diameter D of the center opening of the cap and the length L of the cap is between 1.25 and 3 so that complete combustion may be ensured.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view ofa combustion apparatus in accordance with the present invention;

FiG. 2A is a fragmentary view thereof illustrating the fuel-air mixing section;

FIG. 2B is a side view thereof;

FIG. 2C is a view illustrating vanes or air swirling vanes thereof;

FIG. 3 is a view used for the explanation of the mode of dispersion of atomized fuel particles;

FIG. 4 is a perspective view of an inner air duct with inner air swirling vanes;

FIG. 5 is a graph used for the explanation of the combustions when the angles e and 6 indicated in FIGS. 2A and 2B are varied;

FIGS. 6A and 6B are views used for the explanation of air and atomized fuel particle flows;

FIG. 7A to FIG. 70 are views used for the explanation of the combustions when the ratio between a diameter of a center opening of a cap and a length thereof is varied; and

FIG. 8 is a graph illustrating the combustion conditions shown in FIGv 7A to FIG. 7D.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring FIG. I, the left end of a large-diameter air duct l communicates with the discharge port of a blower (not shown) while the other end is connected to an outer air duct 2 with a tapered portion 20. An inner air duct 3 is supported by a plurality of brackets 31) within the outer air duct 2 coaxially thereof. An ul trasonic vibrator 4 is attached to a horn 5 which is adapted to amplify the ultrasonic vibration. The horn 5 is supported coaxially of the outer air duct 2 by a plurality of brackets or legs 7 which are fixed to the nodal point of the horn 5 and the vibrator 4.

As best shown in FIG. 2B, a plurality of air swirling vanes 9 are extended inwardly from the inner surface of the inner air duct 3, and the free ends of these air swirling vanes 9 define an annular space between them and the horn 5 so as to flow air along the outer surface of the horn 5.. The vanes 9 are extended in such a way that they are tangent to the outer circular boundary of the annular space 30. Between the outer air duct 2 and the inner air duct 3 are disposed equiangularly a plurality of tangential air swirling vanes 8 which are tangential to the inner air duct 3 as best shown in FIG. 28.

Referring back to FIG. I, fuel supply from a fuel tank (not shown) to the horn 5 through a fuel feed pipe I] is controlled by a fuel flow regulator 10. A fuel supply passage 12 is extended along the axis of the horn 5 to flow the fuel supplied from the fuel feed pipe II to a fuel atomizing surface at the free end of the horn 5. An ultrasonic frequency generator 14 is connected through lead lines I3 to a coil 13a mounted on the ultrasonic vibrator 4 to cause the latter to vibrate at ultrasonic frequencies.

To the open end of the outer air duct 2 is attached a frustoconical cap 15 consisting of an outwardly diverged or tapered portion 15a and an opening restricting portion 16, which is radially inwardly bent from the outer edge of the tapered portion 150.

Next, the mode of operation will be described herein after. Fuel whose flow is controlled by the fuel flow regulator 10 is supplied to the atomizing surface 5a at the free end of the horn S, and fuel forms a thin film over the atomizing surface 5a due to the surface tension and viscosity of the fuel. A thin fuel film formed upon the atomizing surface 5a is broken into finely divided particles due to the ultrasonic vibration of the horn 5, and the finely divided or atomized fuel particles are scattered forwardly from the atomizing surface 5a. However, the atomization of fuel only by the ultrasonic vibration of the horn 5 results in a densely concentrated zone a in FIG. 3 just in the proximity of the atomizing surface 5a and a thinly concentrated Zone b away from the atomizing surface 5a. The atomized fuel particles tend to fall in the proximity of the atomizing surface. Thus, a preferable pattern of atomized fuel particle distribution cannot be obtained. To overcome these problems the blower (not shown) is provided to force the atomized fuel particles to scatter forwardly from the atomizing surface by the air passing through the large diameter air duct 1 and the outer air duct 2. Furthermore, according to the present invention, the outer and inner air swirling vanes 8 and 9 and the cap 15 are provided to form the optimum ignition zone.

As shown in FIG. 1, air which reaches the smalldiameter section of the outer air duct 2 is divided into the air flow A passing through the annular space between the horn 5 and the tips of the vanes 9, the air flow B passing through the inner air duct 3 and the air flow C passing through the annular space between the outer and inner air ducts 2 and 3. The air flow A passing through the annular space 3a serves to force the atomized fuel particles away from the atomizing surface a. The air flow B passing through the inner air duct 3 is swirled by the air swirling vanes 9 and joined to the air flow A passing through the annular space 30 thereby swirling and mixing the atomized fuel particles with air. The air flow B further serves to force the atomized fuel particles away from the atomizing surface 5a. Unlike the conventional apparatus, the free ends of the air swirling vanes 3 in the inner air duct 3 are not brought into contact with the outer surface of the horn 5 but instead terminate at a slight distance therefrom. thereby defining the annular space 30, The air flow passing through the annular space 3a is therefore not separated from the air flow passing through the inner air duct 3 and the fuel and air are well mixed with each other. Therefore there is produced no vortex which adversely affects the mixing of the atomized fuel particles with air. Furthermore, the atomized fuel particles dispersed away from the swirling air flow consisting of the air flow A passing through the annular space 3a and the air flow B passing through the inner air duct 2 may be swirled by the swirling air flow C passing through the space between the outer and inner air ducts 2 and 3 so that the atomized fuel particles may be well mixed with air.

In order to attain the optimum combustion, the atomized fuel particles must be uniformly distributed in air, and a suitable ignition zone must be formed in a suitable pattern and at a suitable location so that the normal combustion may be continued. For this purpose, the velocities and the direction of swirling of the air flows must be so determined as to form such optimum ignition zone. If the velocity of the air flow A passing through the annular space 3a is too great, the velocity of atomized fuel particles in the direction of the axis of the horn exceeds the combustion speed, resulting in leaping flames. On the other hand, if the velocity of the air flow is too slow, the flame is drawn backwardly of the atomizing surface 5a due to the negative pressure produced by the air swirling vanes 9 within the inner air duct 3, thus resulting in backfire and the accumulation of carbon upon the atomizing surface 50. Furthermore, when the air flows A, B and C collide in the ignition zone, the vortexes which adversely affect combustion are produced. Since the vortexes tend to move from one place to another, the fuel particle pattern also drifts resulting in fluctuation and instability of the flames and increased noise.

To overcome these problems. according to the present invention, the outwardly diverging cap a is attached to the open end of the outer air duct 2, and the relation between the angle between the tapered mrtion 15a and the axis of the horn 5 and the angle of the outer air swirling vanes 8 is so determined as to satisfy some conditions to be described in more detail hereinafter.

As shown in FIG. 2C, the angle between the outer and inner air swirling vanes 8 and 9 and the axis of the inner air duct 3 is designated by 6,, and as shown in FIG. 2A angle of the tapered portion 15a of the cap 15 with respect to the axis thereof is designated by 6 According to the extensive experiments conducted by the inventor, these angles 6, and 6 are correlated as shown in FIG. 5.

Referring to FIG. 5, the straight line Y, is expressed y 3 2 IO i and the straight line Y, is given by When the angle 0, is less than 10, no advantage is obtained in practice. The P area enclosed by the straight line Y, and the 6, axis indicates a noncombustion area. The 0 area between the straight lines Y, and Y indicates a complete combustion area, and the R area enclosed by the straight line Y and the 9 axis indicates an incomplete combustion area.

Referring to FIGS. 6A and 6B, the air flow is indicated by the solid lines while the directions of the drift of atomized fuel particles are indicated by the broken lines. The condition shown in FIG. 6A corresponds to the P area in FIG. 5 and the condition shown in FIG. 6B, the R area. In FIG. 6A, the angle 0 is too small with respect to the angle 6,, so that atomized fuel particles are forced to impinge against the inner wall of the cap 15 by the strong swirling air flows within the cap 15. The impinged atomized fuel particles turn into liquid fuel which is carried out forwardly by the air flow, thus resulting in incomplete combustion. When the angle 6 is too small, the radial component of the swirling air flow is reduced while the axial component is increased, so that the air flow will not expand in the radial direction as indicated by the solid lines in FIG. 6A in front of the cap 15.

In the FIG. 6B, the angle 6 is too large with respect to the angle 6,, so that atomized fuel particles are not imparted with sufficient energies to strike against the inner wall of the cap IS even though they are swirled within the cap 15. Therefore, the quantity of unburnt atomized fuel particles is decreased, but the atomized fuel particles are not mixed with the air in the proximity of the boundary of the swirling air flow. In other words, the air discharged from the cap is not sufficiently mixed with atomized fuel particles, thus resulting in the incomplete combustion.

So far, the angles of the outer and inner air swirling vanes 8 and 9 have been described as being equal to each other, but they may be different.

As described hereinbefore, the angles 6, and 6 are correlated as far as the combustion is concerned so that they must satisfy some conditions. Furthermore, the length L of the cap 15 and the diameter D of its opening 1517 must also satisfy some conditions. The correla tions between the length L and the diameter D obtained by the extensive experiments conducted by the inventor is shown in FIGS. 7A 7D. FIG. 7A shows the correlation when both the length L and the diameter D are smaller. Since the swirling air flow is not sufficiently attenuated or damped within the cap 15 and the diameter D is small, the air flow discharged out of the cap suddenly expands in a radial direction, thus resulting in a ball-shaped flame. Since the axial component of the energy of the swirling air flow is smaller than the radial component, air cannot sufficiently penetrate into a body of atomized fuel particles so that sufficient mixing between the air and atomized fuel particles cannot be attained, thus resulting in the incomplete combustion.

In FIG. 7B, the length L is shorter but the diameter D is greater so that the axial component is stronger, but

the axial component is not attenuated or damped sufficiently Therefore. an incquilibrium between the axial and radial components very frequently occurs in front of the cap so that the flame tends to be broken, resulting in leaping flames.

In FIG. 7C, the length L is longer and the diameter D is smaller so that the air flow discharged out of the cap 15 is unduly reduced. Thus. the air flow fluctuates with the result of blow-off." When the diameter D is too small, atomized fuel particles strike against the inner surface of the opening reducing portion 16 and turn into liquid fuel, thus resulting in incomplete combustion.

In FIG. 7C. the length L is longer and the diameter D is also greater so that the radial component is excessively attenuated while the axial component is in creased, thus resulting in an extraordinarily long flame with a small cross section. In the downstream areas the axial component is decreased so that the mixing of atomized fuel particles with air cannot be carried out in a satisfactory manner. As a result, incomplete combustion occurs and soot is produced from the end of the flame.

The combustion conditions described hereinbefore with reference to FIGS. 7A 7D are illustrated in FIG. 8 for the sake of comparison. The hatched area denotes the ratio between the angies 6 and 6 the ratio between the length L and the diameter D which ensure the optimum combustion. That is, the optimum ratio of the angle 9 to the angle 9 minus 10 is between 3/10 and unity when the ratio D/L is varied within the optimum range between 1.25 and 3.

In FIG. 8, the hatched area indicates a range in which 8 /6 minus l0 3/10 to l and 13/1. L25 to 3. At the point P in the hatched area, 6 3 45", 6 and D/L 2.8, and at the point Q. 0 60, 6 30 and DH, 2. The regions or areas indicated by FIG. 7A. 7B. 7C and 7D in P16. 8 show the areas or regions where the combustions as shown in FIGS. 7A, 7B, 7C and 7D occur respectively.

The optimum conditions for generating 4,000 40.000 Kcal/iiour are 0 45, 20", D r; 70 mm and L mm. in the combustion apparatus with the ultrasonic vibrator and the outer and inner air swirling vanes, the correlations between H and 6 and D and L described above are heid regardless of the positions and configurations of other component parts.

What is claimed is:

1.. in a combustion apparatus of the type comprising an outer air duct with a liquid fuel atomizing horn which is vibrated by an ultrasonic vibrator housed within said outer air duct coaxially thereof,

an inner air duct located within said outer air duct coaxialiy thereof between the front portion of said horn and said outer air duct.

inner air swirling vanes located within said inner air duct, outer air swirling vanes located within said inner and outer air ducts. and

an outwardly diverging cone-shaped cap attached to the front end of said outer air duct. the front portion of said cone-shaped cap being radially inwardly bent to define a center opening,

the improvement wherein the radially inner ends of said inner air swirling vanes are spaced apart from each other and are spaced from said horn to define a space between said horn and said inner air swirling vanes, whereby the spaces between said inner air swirling vanes are open to said space between said horn and inner swirling vanes, and the radially outer ends of said swirling vanes are on the inner peripheral wall of said inner air duct,

the ratio 6 /6 minus 1 being between 3/10 and unity,

wherein 6 is the angle between said inner and outer air swirling vanes and the axis of said horn and 6 is the angle between the tapered portion of said cap and said axis of said horn.

2. A combustion apparatus as defined in claim 1 wherein the ratio of a diameter D of said center opening of said cap to the length L in the axial direction between the open end of said outer air duct and the front end of said cap is between 1.25 and 3.

3. A combustion apparatus as defined in claim 2 wherein 6 45, 8 20, D mm and L 25 mm.

4. In a combustion apparatus of the type comprising an outer air duct with a liquid fuel atomizing horn which is vibrated by an ultrasonic vibrator housed within said outer air duct coaxially thereof.

an inner duct located within said outer air duct coaxially thereof between the front portion of said horn and said outer air duct,

inner air swirling vanes located within said inner air duct,

outer air swirling vanes located between said inner and outer air ducts and an outwardly diverging coneshaped cap attached to the front end of said outer air duct, the front por tion of said cone-shaped cap being radially inwardly bent to define a center opening,

the improvement wherein the radially inner ends of said inner air swirling vanes are spaced apart from each other and are spaced from said horn to define a space between said horn and said inner air swirling vanes, whereby the spaces between said inner air swirling vanes are open to said space between said horn and inner swirling vanes, and the radially outer ends of said inner swirling vanes are on the inner peripheral wall of said inner air duct.

the ratio of the diameter D of said center opening of said cap to the length L in the axial direction between the open end of said outer air duct and the front end of said cap being between 1.25 and 3. 

1. In a combustion apparatus of the type comprising an outer air duct with a liquid fuel atomizing horn which is vibrated by an ultrasonic vibrator housed within said outer air duct coaxially thereof, an inner air duct located within said outer air duct coaxially thereof between the front portion of said horn and said outer air duct, inner air swirling vanes located within said inner air duct, outer air swirling vanes located within said inner and outer air ducts, and an outwardly diverging cone-shaped cap attached to the front end of said outer air duct, the front portion of said cone-shaped cap being radially inwardly bent to define a center opening, the improvement wherein the radially inner ends of said inner air swirling vanes are spaced apart from each other and are spaced from said horn to define a space between said horn and said inner air swirling vanes, whereby the spaces between said inner air swirling vanes are open to said space between said horn and inner swirling vanes, and the radially outer ends of said swirling vanes are on the inner peripheral wall of said inner air duct, the ratio theta 2/ theta 1 minus 1 being between 3/10 and unity, wherein theta 1 is the angle between said inner and outer air swirling vanes and the axis of said horn and theta 2 is the aNgle between the tapered portion of said cap and said axis of said horn.
 2. A combustion apparatus as defined in claim 1 wherein the ratio of a diameter D of said center opening of said cap to the length L in the axial direction between the open end of said outer air duct and the front end of said cap is between 1.25 and
 3. 3. A combustion apparatus as defined in claim 2 wherein theta 1 45*, theta 2 20*, D 70 mm and L 25 mm.
 4. In a combustion apparatus of the type comprising an outer air duct with a liquid fuel atomizing horn which is vibrated by an ultrasonic vibrator housed within said outer air duct coaxially thereof, an inner duct located within said outer air duct coaxially thereof between the front portion of said horn and said outer air duct, inner air swirling vanes located within said inner air duct, outer air swirling vanes located between said inner and outer air ducts and an outwardly diverging cone-shaped cap attached to the front end of said outer air duct, the front portion of said cone-shaped cap being radially inwardly bent to define a center opening, the improvement wherein the radially inner ends of said inner air swirling vanes are spaced apart from each other and are spaced from said horn to define a space between said horn and said inner air swirling vanes, whereby the spaces between said inner air swirling vanes are open to said space between said horn and inner swirling vanes, and the radially outer ends of said inner swirling vanes are on the inner peripheral wall of said inner air duct, the ratio of the diameter D of said center opening of said cap to the length L in the axial direction between the open end of said outer air duct and the front end of said cap being between 1.25 and
 3. 